As an example of a use of a display screen separator line reference is made to the 3270 family of display terminals manufactured by the International Business Machines Corporation. The 3270 family terminal is used as one of a cluster of online display stations, connected to one or more System/370 host computers, and employs a 3270 data stream to interact with host programs (System/370 is a Trademark of the International Business Machines Corporation of Armonk, N.Y.). This type of host-dependent display station is generally referred to as a Mainframe Interactive (MFI) terminal.
Referring to FIG. 1 there is shown a typical MFI display screen 1 being used in an alphanumeric text display mode, as opposed to a graphical display mode. Display screen is divided into two areas by a horizontal separator line 2. A first area is referred to as a display or host data area 3 and a second area is referred to as an Operator Information Area (OIA) 4. The OIA 4 occupies, by convention, a bottom alphanumeric text row of the screen 1. The OIA 4 is employed to display various operating and status indicators that are associated with the terminal operation and with communication with the host computer(s). The separator line 2 visually separates the OIA 4 from the display area 3. For a color display, and by convention in the 3270 family of display terminals, the separator line 2 is displayed as a continuous blue line that is one screen scan line in width.
However, a problem is created if it is desired to emulate the operation and appearance of the 3270 terminal screen display with a data processor, such as a personal computer. By example, it may be desired to emulate the 3270 terminal display with a Personal System/2 data processor having a Video Graphics Array (VGA) display controller (Personal System/2 is a Registered Trademark of the International Business Machines Corporation of Armonk, N.Y.). Also by example, it may be desired to accomplish a 3270 emulation with a data processor that includes an Extended Graphics Adapter (EGA) display controller or that includes an Extended Graphics Array (XGA) display controller operating in a VGA compatibility mode.
The problem arises due to a lack of specialized hardware, on these and other existing display controllers, to create the separator line 2. As a result, no known type of 3270 emulator has accurately emulated a separator line 2 between the display area 3 and the OIA 4.
One possible method of emulating the separator line 2 would be accomplished in an All Points Addressable (APA) graphics mode through the use of software. However, the use of APA for generating the separator line 2 is undesirable in that a visible performance degradation would occur when drawing text characters in APA mode.
A possible approach to emulating the separator line 2 in the alphanumeric text mode would employ an entire alphanumeric row to display the separator line 2. However, in that the 3270 family of terminals employs only a single scan line for the separator line 2, as opposed to the plurality of scan lines that comprise an alphanumeric row, an inconsistent screen appearance would result. Furthermore, it would be undesirable to dedicate an entire alphanumeric row for generating the separator line 2, as this would reduce by one the number of displayable alphanumeric rows in the display area 3.
Another approach, which would add an overscore to the fonts displayed within the OIA 4, is also undesirable for a number of reasons.
It is therefore an object of the invention to provide a method that employs, without modification, existing display controller circuitry to generate a horizontal separator line between two screen areas.
It is a further object of the invention to provide a method for emulating a 3270 screen format on a data processor having a VGA, EGA, or XGA display controller that does not include circuitry specifically provided for generating the separator line.